GENEVA (Reuters) - A 100-carat yellow diamond has sold for 14.5 million Swiss francs (9.69 million pounds) to a private buyer, the star lot in a Geneva jewelry sale that Sotheby's auction house said fetched 125.5 million francs overall.

The "Graff Vivid Yellow", weighing 100.09 carats, set a record for a yellow diamond, the chairman of Sotheby's Switzerland, David Bennett, said in a statement on Wednesday after Tuesday's sale.

"With its exceptional size and a superb daffodil color, the Graff Vivid Yellow is a truly extraordinary diamond with immense presence," Bennett said.

However, the gem failed to hit the bottom end of its estimate, with a hammer price of 12.8 million francs.

Sotheby's had expected that the cushion-shaped diamond, of which neither the seller nor buyer were identified, would reach a hammer price of between 13.4 million and 22.3 million francs.

The total price, which Sotheby's said was equivalent to $163,331 per carat, includes commission fees known as the "buyer's premium". It gave no reason for it missing the estimate.

The auction house said the evening set a world record for a jewelry auction.

It hailed a record for its Geneva sale in November, when it set a world-record price of 76.3 million Swiss francs (then $83 million) for the coveted "Pink Star" diamond. However, it said in February it had acquired the stone after its buyer failed to pay up.

Among the other stellar lots at Tuesday's auction was a white round diamond of 103.46 carats, also cut by Graff and described by Sotheby's as one of the largest brilliant-cut diamonds in the world, which sold for 4.3 million francs.

A smaller but stunning 31.34-carat white diamond, "The Victory Diamond" which belonged to Florence Gould, daughter-in-law of the American railroad magnate Jay Gould, had been estimated at $5-$8 million, but failed to sell.